1. Field of the Invention
The present invention relates, in general, to a fuel injection system used for injecting fuel into the combustion chamber of an internal combustion engine and, more particularly, to a variable fuel injection system capable of controllably feeding fuel into the combustion chamber by controlling electromotive force applied to a solenoid coil, thus effectively feeding an appropriate amount of fuel to the engine in accordance with an engine load.
2. Description of the Prior Art
FIG. 3 shows the construction of a typical variable fuel injector for internal combustion engines. As shown in the drawing, the injector is comprised of an injector body 11. An internal passage 12 is axially formed in the body 11 and is connected to a fuel pump, while an injection nozzle 13 is formed at the tip of the body 11. The nozzle 13 communicates with the internal passage 12, thus injecting fuel under pressure. A needle valve 14 is interiorly provided in the body 11 at a position around the nozzle 13 so as to selectively close the nozzle 13. A plunger 15 is integrated with the top end of the needle valve 14 and is movably received in the body 11. The plunger 15, with the needle valve 14, is selectively moved in the body 11 under the control of a solenoid coil 16, thus opening or closing the nozzle 13. The plunger 15 is normally biased by a return spring 17, thus being elastically returned to its original position when the solenoid coil 16 is turned off. At the original position, the plunger 15 allows the needle valve 14 to close the nozzle 13. Provided at the inlet end of the internal passage 12 of the injector body 11 is a filter 18 used for filtering fuel.
When the solenoid coil 16 is turned on, the coil 16 forms an electromagnet, thus retracting the plunger 15 in the body 11. Therefore, the needle valve 14 opens the nozzle 13.
When the nozzle 13 is opened as described above, pressurized fuel is injected from the injector body 11 into the combustion chamber of an engine through the nozzle 13.
On the other hand, when the solenoid coil 16 is turned off, a magnetic field is removed from the coil 16, thus removing any external force from the plunger 15. The plunger free from any external force is elastically returned to its original position due to the restoring force of the return spring 17, thus allowing the needle valve 14 to close the nozzle 13. In such a case, the injector does not inject the pressurized fuel into the combustion chamber.
Therefore, the amount of injected fuel of the above injector is determined by the length of time the solenoid coil is turned on, thus opening the nozzle. The typical injector fails to appropriately control the amount of injected fuel in accordance with an engine load, thereby overly consuming fuel and increasing the amount of the harmful exhaust gas of an engine.